During the last decade, the internal combustion engine industry has more and more been forced to look into the problems related to the exhaust emission. The development is characterized by an increased, international legislative pressure on today's internal combustion engines for vehicles, in order to obtain lower and lower emission contents of CO, HC and NO.sub.x, as well as of particles and noise.
National, comparatively uncomplicated testing cycles were first developed, simulating statistically established load sequences for engines in urban traffic. In connection with these test sequences, the contents of impurities in the exhaust gases were measured, and subsequently compiled in accordance with given rules or standards. These methods made possible an adjustment of the engine fuel supply system to low emissions within the tested, transient ranges and thus not giving a correct picture of the conditions during actual operation.
For that reason, it was, in some countries, decided to use a more complicated testing sequence, and simultaneously to take samples representing the accumulated emission in units of weight per distance for vehicles running in accordance with the new test cycle. One new testing sequence takes about 23 minutes to run, and requires a special gas sampling unit and a qualified gas analysis equipment, together with a chassi-dynamometer. The investment value of such an arrangement is, today, about $200,000 per unit, including erection and mechanical and analytical equipment.
This has created an instrument making it possible to check the cars produced and delivered, but is not convenient for practical supervision of the existing car park not, for example, it is evident that individual supervision of a large car park is impossible, if each test requires about half an hour for analysis, while at the same time qualified personnel and equipment is tied up for the same period. It are therefore important to find test procedures, which can make a rapid gas analysis possible. Carbon oxide tests have for some years been taken in connection with idling running during the annual checking of the Swedish car park. The idling sequence is, however, only part of the aforementioned cycles, and has the disadvantage that no content of nitrogen oxide can be traced, which can be correlated to the contents in the actual cycles. Neither are correlations between HC contents during idling, and HC contents during driving cycles satisfactory. In the international literature simplified driving cycles can be found directed toward making a simple supervision possible, but their common characteristics are that they require engine lead during controllable conditions on a chassi-dynamometer. The main part of the investment, discussed earlier, as well as the instrumentation requirements will remain, even if testing time might be reduced.